Bismuth ferrite (BiFeO3) is an attractive multiferroic material, extensively explored in photoferroelectric investigations. However, its applications are hindered by the high leakage current, requiring precise control of charge transport properties. Defect engineering has emerged as a promising strategy to address this issue: controlling the defect chemistry, particularly oxygen vacancies, is key to tuning the electrical properties. This study investigates the influence of 5% - and 2% -doping on the dark and light-induced charge transport properties of polycrystalline BiFeO3 films. Our results demonstrate that reduces dark conductivity by decreasing oxygen vacancy concentration with no change in the physical nature of the charge transport mechanism. In contrast, modifies the charge transport mechanism, increasing low-field (E 100 kVcm-1) dark conductivity while drastically reducing high-field (E 250 kVcm-1) dark conductivity. This tuning of the defect chemistry is also key to enhance the photovoltages of the bulk photovoltaic effect in BiFeO3. High photoinduced electric fields up to 7 kVcm-1 and low photoconductivity values are obtained with -doping, while high short-circuit photocurrent values are obtained with -doping.
{"title":"Defect engineering of charge transport and photovoltaic effect in BiFeO3 films","authors":"Alfredo Blázquez Martínez , Barnik Mandal , Sebastjan Glinsek , Torsten Granzow","doi":"10.1016/j.actamat.2024.120481","DOIUrl":"10.1016/j.actamat.2024.120481","url":null,"abstract":"<div><div>Bismuth ferrite (BiFeO<sub>3</sub>) is an attractive multiferroic material, extensively explored in photoferroelectric investigations. However, its applications are hindered by the high leakage current, requiring precise control of charge transport properties. Defect engineering has emerged as a promising strategy to address this issue: controlling the defect chemistry, particularly oxygen vacancies, is key to tuning the electrical properties. This study investigates the influence of 5% <figure><img></figure> - and 2% <figure><img></figure> -doping on the dark and light-induced charge transport properties of polycrystalline BiFeO<sub>3</sub> films. Our results demonstrate that <figure><img></figure> reduces dark conductivity by decreasing oxygen vacancy concentration with no change in the physical nature of the charge transport mechanism. In contrast, <figure><img></figure> modifies the charge transport mechanism, increasing low-field (E <span><math><mo><</mo></math></span> 100<!--> <!-->kVcm<sup>-1</sup>) dark conductivity while drastically reducing high-field (E <span><math><mo>></mo></math></span> 250<!--> <!-->kVcm<sup>-1</sup>) dark conductivity. This tuning of the defect chemistry is also key to enhance the photovoltages of the bulk photovoltaic effect in BiFeO<sub>3</sub>. High photoinduced electric fields up to 7<!--> <!-->kVcm<sup>-1</sup> and low photoconductivity values are obtained with <figure><img></figure> -doping, while high short-circuit photocurrent values are obtained with <figure><img></figure> -doping.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"283 ","pages":"Article 120481"},"PeriodicalIF":8.3,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142452658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-22DOI: 10.1016/j.actamat.2024.120501
Xinkai Wang , Qiankun Yang , Weisong Wu , Wei Zhang , Yong Zhang , Dingshun Yan , Kefu Gan , Bin Liu , Zhiming Li
We design and investigate a W15Ta15Cr35V35 (at.%) multicomponent alloy (MCA) with exceptional radiation resistance. The sintered WTaCrV alloy exhibits a body-centered cubic (BCC) matrix with dispersed coherent ordered nanoprecipitates. After ∼3-hour irradiation under 400 keV He+ at room temperature (RT) and 450 °C with a fluence of 2 × 1017 ions/cm2, the irradiation hardening values of the MCA are about a quarter of those of pure tungsten counterparts irradiated at identical conditions. Besides, helium bubbles generated in the irradiated matrix of the MCA are much smaller, compared with those in the pure tungsten and other tungsten-rich alloys previously reported. The exceptional radiation resistance of the present WTaCrV alloy can be mainly attributed to two synergistic mechanisms. First, the high lattice distortion of the solid solution matrix promotes the local non-directional diffusion of irradiation defects, effectively suppressing the aggregation of irradiation defects and helium atoms along specific orientations. This facilitates more uniform nucleation of helium bubbles in the alloy matrix. Second, carbon was introduced during fast hot pressing sintering as interstitial solute to form carbon-rich coherent ordered nanoprecipitates. The carbon-vacancy complexes generated in the nanoprecipitates inhibit the nucleation and aggregation of helium atoms at the vacancies during He+ irradiation. The above two mechanisms synergistically enhance the resistance against He+ irradiation. This work thus demonstrates a design strategy for high radiation resistance alloys by introducing well-tuned ordered coherent nanoprecipitates in multicomponent alloy systems.
{"title":"Excellent radiation resistance via enforced local non-directional He diffusion in a WTaCrV multicomponent alloy containing coherent ordered nanoprecipitates","authors":"Xinkai Wang , Qiankun Yang , Weisong Wu , Wei Zhang , Yong Zhang , Dingshun Yan , Kefu Gan , Bin Liu , Zhiming Li","doi":"10.1016/j.actamat.2024.120501","DOIUrl":"10.1016/j.actamat.2024.120501","url":null,"abstract":"<div><div>We design and investigate a W<sub>15</sub>Ta<sub>15</sub>Cr<sub>35</sub>V<sub>35</sub> (at.%) multicomponent alloy (MCA) with exceptional radiation resistance. The sintered WTaCrV alloy exhibits a body-centered cubic (BCC) matrix with dispersed coherent ordered nanoprecipitates. After ∼3-hour irradiation under 400 keV He<sup>+</sup> at room temperature (RT) and 450 °C with a fluence of 2 × 10<sup>17</sup> ions/cm<sup>2</sup>, the irradiation hardening values of the MCA are about a quarter of those of pure tungsten counterparts irradiated at identical conditions. Besides, helium bubbles generated in the irradiated matrix of the MCA are much smaller, compared with those in the pure tungsten and other tungsten-rich alloys previously reported. The exceptional radiation resistance of the present WTaCrV alloy can be mainly attributed to two synergistic mechanisms. First, the high lattice distortion of the solid solution matrix promotes the local non-directional diffusion of irradiation defects, effectively suppressing the aggregation of irradiation defects and helium atoms along specific orientations. This facilitates more uniform nucleation of helium bubbles in the alloy matrix. Second, carbon was introduced during fast hot pressing sintering as interstitial solute to form carbon-rich coherent ordered nanoprecipitates. The carbon-vacancy complexes generated in the nanoprecipitates inhibit the nucleation and aggregation of helium atoms at the vacancies during He<sup>+</sup> irradiation. The above two mechanisms synergistically enhance the resistance against He<sup>+</sup> irradiation. This work thus demonstrates a design strategy for high radiation resistance alloys by introducing well-tuned ordered coherent nanoprecipitates in multicomponent alloy systems.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"282 ","pages":"Article 120501"},"PeriodicalIF":8.3,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142486904","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-22DOI: 10.1016/j.actamat.2024.120486
Liangzhao Huang , Thomas Schuler , Chu-Chun Fu , Daniel Brimbal , Frédéric Soisson
This study investigates the thermodynamics and kinetics of the NiCr system, focusing specifically on the kinetics of the order–disorder phase transformation in the Ni–33at.%Cr alloy. Combining density functional theory, CALPHAD-type models, and experimental diffusion data, we introduce and validate an efficient pair interaction model (PIM) and use it in Monte Carlo simulations. Our results include a detailed phase diagram of NiCr in face-centered cubic structure and kinetic models that delineate the behavior of solid solutions at high temperatures and ordered structures at low temperatures. The simulations shed light on tracer diffusion and ordering kinetics within Ni–33at.%Cr, demonstrating good agreement with existing experimental data. Furthermore, our simulation-driven insights prompt a reevaluation of certain aspects of related experimental studies concerning the apparent ordering activation enthalpies and growth kinetics. We also provide a thorough discussion on the strengths of our models and features for future improvement.
{"title":"Thermodynamics and kinetics of long-range ordering in FCC Ni–33at.%Cr alloys: Insights from atomic scale modeling","authors":"Liangzhao Huang , Thomas Schuler , Chu-Chun Fu , Daniel Brimbal , Frédéric Soisson","doi":"10.1016/j.actamat.2024.120486","DOIUrl":"10.1016/j.actamat.2024.120486","url":null,"abstract":"<div><div>This study investigates the thermodynamics and kinetics of the Ni<img>Cr system, focusing specifically on the kinetics of the order–disorder phase transformation in the Ni–33at.%Cr alloy. Combining density functional theory, CALPHAD-type models, and experimental diffusion data, we introduce and validate an efficient pair interaction model (PIM) and use it in Monte Carlo simulations. Our results include a detailed phase diagram of Ni<img>Cr in face-centered cubic structure and kinetic models that delineate the behavior of solid solutions at high temperatures and ordered structures at low temperatures. The simulations shed light on tracer diffusion and ordering kinetics within Ni–33at.%Cr, demonstrating good agreement with existing experimental data. Furthermore, our simulation-driven insights prompt a reevaluation of certain aspects of related experimental studies concerning the apparent ordering activation enthalpies and growth kinetics. We also provide a thorough discussion on the strengths of our models and features for future improvement.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"282 ","pages":"Article 120486"},"PeriodicalIF":8.3,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142486903","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-22DOI: 10.1016/j.actamat.2024.120502
Mo-Rigen He, Arunima Banerjee, Kevin J. Hemker
Nanotwinned Ni-Mo-W alloys possess a combination of unique mechanical and thermal properties, such as ultrahigh strength and microstructural stability, which are correlated with the presence of densely packed growth twins. In a previous study, the ultrahigh compressive strength of Ni84Mo11W5 (atomic percent) micropillars was associated with the formation of highly localized shear bands, but the trigger for such localized plasticity was not identified. Here, Ni86Mo3W11 (atomic percent) micropillars were carefully compressed to various levels to uncover the nanoscale deformation mechanisms that trigger the strain localization. Post-mortem transmission electron microscopy investigations of pillars after the first measurable strain burst revealed ∼50 nm thick shear bands consisting of reoriented and twin-free grains, while the columnar grains adjacent to the shear bands were partly detwinned. More importantly, unlike the Mo-rich pillars, the W-rich pillars showed discernible plasticity before the first strain burst. Close inspection made before the formation of a mature shear band revealed a detwinning region of ∼30 nm thickness that aligned more parallel to the coherent twin boundaries, and multiple nanotwins truncated with incoherent twin boundaries were resolved between the detwinning band and the nanotwinned grains. These observations strongly suggest detwinning, facilitated by migration of incoherent twin boundaries, to be the precursor to strain localization and the intensive shear banding observed in nanotwinned Ni-Mo-W alloys. Comparing the present results with the literature further highlights the general role of detwinning in governing the plastic behavior of nanotwinned alloys with a wide range of stacking fault energy.
{"title":"The deformation mechanisms responsible for strain localization in nanotwinned nickel alloys","authors":"Mo-Rigen He, Arunima Banerjee, Kevin J. Hemker","doi":"10.1016/j.actamat.2024.120502","DOIUrl":"10.1016/j.actamat.2024.120502","url":null,"abstract":"<div><div>Nanotwinned Ni-Mo-W alloys possess a combination of unique mechanical and thermal properties, such as ultrahigh strength and microstructural stability, which are correlated with the presence of densely packed growth twins. In a previous study, the ultrahigh compressive strength of Ni<sub>84</sub>Mo<sub>11</sub>W<sub>5</sub> (atomic percent) micropillars was associated with the formation of highly localized shear bands, but the trigger for such localized plasticity was not identified. Here, Ni<sub>86</sub>Mo<sub>3</sub>W<sub>11</sub> (atomic percent) micropillars were carefully compressed to various levels to uncover the nanoscale deformation mechanisms that trigger the strain localization. Post-mortem transmission electron microscopy investigations of pillars after the first measurable strain burst revealed ∼50 nm thick shear bands consisting of reoriented and twin-free grains, while the columnar grains adjacent to the shear bands were partly detwinned. More importantly, unlike the Mo-rich pillars, the W-rich pillars showed discernible plasticity before the first strain burst. Close inspection made before the formation of a mature shear band revealed a detwinning region of ∼30 nm thickness that aligned more parallel to the coherent twin boundaries, and multiple nanotwins truncated with incoherent twin boundaries were resolved between the detwinning band and the nanotwinned grains. These observations strongly suggest detwinning, facilitated by migration of incoherent twin boundaries, to be the precursor to strain localization and the intensive shear banding observed in nanotwinned Ni-Mo-W alloys. Comparing the present results with the literature further highlights the general role of detwinning in governing the plastic behavior of nanotwinned alloys with a wide range of stacking fault energy.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"282 ","pages":"Article 120502"},"PeriodicalIF":8.3,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142452593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-22DOI: 10.1016/j.actamat.2024.120482
Alexander F. Chadwick , Juan Guillermo Santos Macías , Arash Samaei , Gregory J. Wagner , Manas V. Upadhyay , Peter W. Voorhees
Integrating experiment and simulation provides invaluable insights into the critical parameters that determine the microstructure of alloys produced by additive manufacturing. Here, the grain structure formation due to solidification during single pass laser scans (mimicking bead-on-plate single tracks) on a 316L stainless steel is studied in situ inside a scanning electron microscope that is directly integrated with a continuous-wave laser. The grain size distribution before melting is used as an initial condition in a coupled phase-field/thermal multiphysics modeling framework. The predicted resolidified microstructures are found to agree favorably with those observed experimentally for multiple laser powers and scan velocities, indicating the validity of the overall model. Grain morphology is analyzed quantitatively, and the top surfaces are compared between the experiments and simulations. Analysis of the three-dimensional grain shapes predicted by the simulations shows that the length of the major axis of the resolidified grains is sensitive to laser power and scan speeds, while the length of the minor axis is not. Furthermore, the preferential alignment of the major axes of the grains depends on the melt pool geometry.
{"title":"On microstructure development during laser melting and resolidification: An experimentally validated simulation study","authors":"Alexander F. Chadwick , Juan Guillermo Santos Macías , Arash Samaei , Gregory J. Wagner , Manas V. Upadhyay , Peter W. Voorhees","doi":"10.1016/j.actamat.2024.120482","DOIUrl":"10.1016/j.actamat.2024.120482","url":null,"abstract":"<div><div>Integrating experiment and simulation provides invaluable insights into the critical parameters that determine the microstructure of alloys produced by additive manufacturing. Here, the grain structure formation due to solidification during single pass laser scans (mimicking bead-on-plate single tracks) on a 316L stainless steel is studied <em>in situ</em> inside a scanning electron microscope that is directly integrated with a continuous-wave laser. The grain size distribution before melting is used as an initial condition in a coupled phase-field/thermal multiphysics modeling framework. The predicted resolidified microstructures are found to agree favorably with those observed experimentally for multiple laser powers and scan velocities, indicating the validity of the overall model. Grain morphology is analyzed quantitatively, and the top surfaces are compared between the experiments and simulations. Analysis of the three-dimensional grain shapes predicted by the simulations shows that the length of the major axis of the resolidified grains is sensitive to laser power and scan speeds, while the length of the minor axis is not. Furthermore, the preferential alignment of the major axes of the grains depends on the melt pool geometry.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"282 ","pages":"Article 120482"},"PeriodicalIF":8.3,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142486905","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-21DOI: 10.1016/j.actamat.2024.120498
Shuhei Yoshida , Rui Fu , Wu Gong , Takuto Ikeuchi , Yu Bai , Zongqiang Feng , Guilin Wu , Akinobu Shibata , Niels Hansen , Xiaoxu Huang , Nobuhiro Tsuji
Face-centered cubic (FCC) high/medium entropy alloys (HEAs/MEAs), novel multi-principal element alloys, are known to exhibit exceptional mechanical properties at room temperature; however, the origin is still elusive. Here, we report the deformation microstructure evolutions in a tensile-deformed Co20Cr40Ni40 representative MEA and Co60Ni40 alloy, a conventional binary alloy for comparison. These FCC alloys have high/low friction stresses, fundamental resistance to dislocation glide in solid solutions, respectively, and share similar other material properties, including stacking fault energy. The Co20Cr40Ni40 MEA exhibited higher yield strength and work-hardening ability than in the Co60Ni40 alloy. Deformation microstructures in the Co60Ni40 alloy were marked by the presence of coarse dislocation cells (DCs) regardless of grain orientation and a few deformation twins (DTs) in grains with the tensile axis (TA) near 〈1 1 1〉. In contrast, the MEA developed three distinct deformation microstructures depending on grain orientations: fine DCs in grains with the TA near 〈1 0 0〉, planar dislocation structure (PDS) in grains with other orientations, and a high density of DTs along with PDS in grains oriented 〈1 1 1〉. Three-dimensional electron tomography revealed that PDS in the MEA confined dislocations within specific {1 1 1} planes, indicating suppression of cross-slip of screw dislocations and dynamic recovery. In-situ X-ray diffraction during tensile deformation showed a higher dislocation density in the MEA than in the Co60Ni40 alloy. These findings demonstrate that FCC HEAs/MEAs with high friction stresses naturally develop unique deformation microstructures which is beneficial for realizing superior mechanical properties compared to conventional materials.
面心立方（FCC）高/中熵合金（HEAs/MEAs）是一种新型多主元素合金，在室温下表现出优异的机械性能，但其起源至今仍是个谜。在此，我们报告了拉伸变形 Co20Cr40Ni40 代表性 MEA 和 Co60Ni40 合金（一种传统的二元合金）的形变微观结构演变，以作比较。这些催化裂化合金分别具有高/低摩擦应力，在固溶体中具有基本的抗位错滑行能力，并具有相似的其他材料特性，包括堆积断层能。与 Co60Ni40 合金相比，Co20Cr40Ni40 MEA 具有更高的屈服强度和加工硬化能力。Co60Ni40 合金的变形微观结构特点是，无论晶粒取向如何，都存在粗大的位错单元（DC），在拉伸轴（TA）靠近<1 1 1>的晶粒中存在少量变形孪晶（DT）。相反，根据晶粒取向的不同，MEA 形成了三种截然不同的形变微观结构：在 TA 接近<1 0 0>的晶粒中形成细小的 DC，在其他取向的晶粒中形成平面位错结构 (PDS)，在取向<1 1 1>的晶粒中形成高密度的 DT 和 PDS。三维电子断层扫描显示，MEA 中的 PDS 将位错限制在特定的 {1 1 1} 平面内，表明螺位错的交叉滑移和动态恢复受到抑制。拉伸变形过程中的原位 X 射线衍射显示，MEA 中的位错密度高于 Co60Ni40 合金。这些研究结果表明，具有高摩擦应力的催化裂化HEA/MEA会自然形成独特的变形微观结构，这有利于实现优于传统材料的机械性能。
{"title":"Characteristic deformation microstructure evolution and deformation mechanisms in face-centered cubic high/medium entropy alloys","authors":"Shuhei Yoshida , Rui Fu , Wu Gong , Takuto Ikeuchi , Yu Bai , Zongqiang Feng , Guilin Wu , Akinobu Shibata , Niels Hansen , Xiaoxu Huang , Nobuhiro Tsuji","doi":"10.1016/j.actamat.2024.120498","DOIUrl":"10.1016/j.actamat.2024.120498","url":null,"abstract":"<div><div>Face-centered cubic (FCC) high/medium entropy alloys (HEAs/MEAs), novel multi-principal element alloys, are known to exhibit exceptional mechanical properties at room temperature; however, the origin is still elusive. Here, we report the deformation microstructure evolutions in a tensile-deformed Co<sub>20</sub>Cr<sub>40</sub>Ni<sub>40</sub> representative MEA and Co<sub>60</sub>Ni<sub>40</sub> alloy, a conventional binary alloy for comparison. These FCC alloys have high/low friction stresses, fundamental resistance to dislocation glide in solid solutions, respectively, and share similar other material properties, including stacking fault energy. The Co<sub>20</sub>Cr<sub>40</sub>Ni<sub>40</sub> MEA exhibited higher yield strength and work-hardening ability than in the Co<sub>60</sub>Ni<sub>40</sub> alloy. Deformation microstructures in the Co<sub>60</sub>Ni<sub>40</sub> alloy were marked by the presence of coarse dislocation cells (DCs) regardless of grain orientation and a few deformation twins (DTs) in grains with the tensile axis (TA) near 〈1 1 1〉. In contrast, the MEA developed three distinct deformation microstructures depending on grain orientations: fine DCs in grains with the TA near 〈1 0 0〉, planar dislocation structure (PDS) in grains with other orientations, and a high density of DTs along with PDS in grains oriented 〈1 1 1〉. Three-dimensional electron tomography revealed that PDS in the MEA confined dislocations within specific {1 1 1} planes, indicating suppression of cross-slip of screw dislocations and dynamic recovery. In-situ X-ray diffraction during tensile deformation showed a higher dislocation density in the MEA than in the Co<sub>60</sub>Ni<sub>40</sub> alloy. These findings demonstrate that FCC HEAs/MEAs with high friction stresses naturally develop unique deformation microstructures which is beneficial for realizing superior mechanical properties compared to conventional materials.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"283 ","pages":"Article 120498"},"PeriodicalIF":8.3,"publicationDate":"2024-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142452594","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-20DOI: 10.1016/j.actamat.2024.120493
Jiaying Jin , Mengfan Bu , Zhiheng Zhang , Hansheng Chen , Simon P. Ringer , Liang Zhou , Wang Chen , Mi Yan
High-coercivity Nd–Fe–B permanent magnets crucially depend on the deliberate modulation of intergranular phases, notably exemplified by the I4/mcm-tetragonal Nd6Fe13Ga intergranular phase in the Nd–Fe–Ga–B magnet. Particularly, for the Nd–Dy–Fe–Cu–Ga–B magnet containing multiple rare earths (RE) and alloying metals (M), understanding the evolution of RE6(Fe,M)14 intergranular phase becomes more critical in the quest for higher coercivity. Here we design the (Nd,Pr)29.0Dy3.0FebalCu0.5Ga0.5B0.9N1.15 (NCo, Al, Zr, wt.%) as-sintered magnets, where the major RE/Cu/Ga-rich Ia-cubic intergranular phase is agglomerated in triple junctions. These pristine as-sintered magnets are subjected to annealing over a wide temperature range (390∼900 °C for 3 h) and quenching over a wide time range (0.5∼12 h at 460 °C). Through systematic microstructural characterization and first-principle calculation, the intergranular phase transformation from RE/Cu/Ga-rich Ia-cubic to Fe/Ga-rich I4/mcm-tetragonal structure, and accompanying elemental migration is unveiled. During post-sinter annealing, metastable state I firstly occurs, consisting of nanostructured RE/Cu-rich Ia-cubic and I4/mcm-tetragonal lamellas, with the emergence of multi-twins and coherent interface. Then it evolves into metastable state II, consisting of lath-shaped Fe/Cu/Ga-rich I4/mcm-tetragonal structure with fluctuating Fe/Cu concentrations. Simultaneously, metastable state III occurs, exhibiting P6-hexagonal platelets with lower Cu content and reduced crystallographic symmetry. Finally, heightened Fe/Ga diffusion into the lattice of tetragonal phase with synchronous Cu discharge generates the thermodynamically more stable Fe/Ga-rich RE6Fe13Ga phase. The implication of phase transformation pathways on the coercivity is discussed, offering valuable insights into the optimization of RE6(Fe,M)14 intergranular phase and providing further opportunities for enhanced coercivity.
{"title":"Intergranular phase transformation in post-sinter annealed Nd–Dy–Fe–Cu–Ga–B magnet: From Ia3¯-cubic to I4/mcm-tetragonal structure","authors":"Jiaying Jin , Mengfan Bu , Zhiheng Zhang , Hansheng Chen , Simon P. Ringer , Liang Zhou , Wang Chen , Mi Yan","doi":"10.1016/j.actamat.2024.120493","DOIUrl":"10.1016/j.actamat.2024.120493","url":null,"abstract":"<div><div>High-coercivity Nd–Fe–B permanent magnets crucially depend on the deliberate modulation of intergranular phases, notably exemplified by the <em>I</em>4/<em>mcm</em>-tetragonal Nd<sub>6</sub>Fe<sub>13</sub>Ga intergranular phase in the Nd–Fe–Ga–B magnet. Particularly, for the Nd–Dy–Fe–Cu–Ga–B magnet containing multiple rare earths (RE) and alloying metals (M), understanding the evolution of RE<sub>6</sub>(Fe,M)<sub>14</sub> intergranular phase becomes more critical in the quest for higher coercivity. Here we design the (Nd,Pr)<sub>29.0</sub>Dy<sub>3.0</sub>Fe<sub>bal</sub>Cu<sub>0.5</sub>Ga<sub>0.5</sub>B<sub>0.9</sub>N<sub>1.15</sub> (N<img>Co, Al, Zr, wt.%) as-sintered magnets, where the major RE/Cu/Ga-rich <em>I</em>a<span><math><mover><mn>3</mn><mo>¯</mo></mover></math></span>-cubic intergranular phase is agglomerated in triple junctions. These pristine as-sintered magnets are subjected to annealing over a wide temperature range (390∼900 °C for 3 h) and quenching over a wide time range (0.5∼12 h at 460 °C). Through systematic microstructural characterization and first-principle calculation, the intergranular phase transformation from RE/Cu/Ga-rich <em>I</em>a<span><math><mover><mn>3</mn><mo>¯</mo></mover></math></span>-cubic to Fe/Ga-rich <em>I</em>4/<em>mcm</em>-tetragonal structure, and accompanying elemental migration is unveiled. During post-sinter annealing, metastable state I firstly occurs, consisting of nanostructured RE/Cu-rich <em>I</em>a<span><math><mover><mn>3</mn><mo>¯</mo></mover></math></span>-cubic and <em>I</em>4/<em>mcm</em>-tetragonal lamellas, with the emergence of multi-twins and coherent interface. Then it evolves into metastable state II, consisting of lath-shaped Fe/Cu/Ga-rich <em>I</em>4/<em>mcm</em>-tetragonal structure with fluctuating Fe/Cu concentrations. Simultaneously, metastable state III occurs, exhibiting <em>P</em>6-hexagonal platelets with lower Cu content and reduced crystallographic symmetry. Finally, heightened Fe/Ga diffusion into the lattice of tetragonal phase with synchronous Cu discharge generates the thermodynamically more stable Fe/Ga-rich RE<sub>6</sub>Fe<sub>13</sub>Ga phase. The implication of phase transformation pathways on the coercivity is discussed, offering valuable insights into the optimization of RE<sub>6</sub>(Fe,M)<sub>14</sub> intergranular phase and providing further opportunities for enhanced coercivity.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"283 ","pages":"Article 120493"},"PeriodicalIF":8.3,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142451520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-20DOI: 10.1016/j.actamat.2024.120487
Zhixuan Zhang , Yiqi Guan , Qi Huang , Na Li , Chao Yuan , Weili Wang , Weibin Zhang
Traditional carbide ceramics face a sharp trade-off between hardness and toughness, leading to a significantly reduced lifespan under harsh service conditions like wear, impact, corrosion, and high temperatures. The spinodal decomposition leads to the formation of nano-lamellar structures, serving to refine grain sizes, thus paving the way to simultaneously improve the hardness and toughness of composite carbide ceramics. A wide range of composite carbides can be prepared, but their complex microstructure evolution during aging makes performance optimization extremely challenging. In this work, a strategy by combining the multiscale simulations and experiments is proposed to systematically study the influence of the composition and process on the spinodal decomposition structure and performance. Taking (Ti, Zr)C carbide ceramics as a representative example, three distinct compositions of (Ti, Zr)C solid solutions were successfully synthesized via a sol-gel combined with spark plasma sintering method at 1800 °C, guided by thermodynamic calculations. The influence of aging temperature and duration on spinodal decomposition microstructure evolution in (Ti, Zr)C carbide ceramics was studied by integrating phase-field simulations and first-principles calculations with key experimental observations. After spinodal decomposition, numerous nanoscale nodular structures form, accompanied by the generation of dislocations, leading to a significant improvement in both hardness and toughness of the composite carbides. After aging at 1300 °C for 3 h, the composite carbides achieved peak hardness at 2436 HV, accompanied by a fracture toughness of 3.24 MPa·m1/2. This research provides a scientific approach to improving the hardness and toughness of carbide ceramics through spinodal decomposition, offering essential theoretical foundations for microstructural control and synergistic optimization of performance in innovative carbide ceramics.
{"title":"Insight of the microstructure evolution and performance enhancement of spinodal decomposition in (Ti, Zr)C composite carbide ceramics: Multiscale simulation and experimental investigation","authors":"Zhixuan Zhang , Yiqi Guan , Qi Huang , Na Li , Chao Yuan , Weili Wang , Weibin Zhang","doi":"10.1016/j.actamat.2024.120487","DOIUrl":"10.1016/j.actamat.2024.120487","url":null,"abstract":"<div><div>Traditional carbide ceramics face a sharp trade-off between hardness and toughness, leading to a significantly reduced lifespan under harsh service conditions like wear, impact, corrosion, and high temperatures. The spinodal decomposition leads to the formation of nano-lamellar structures, serving to refine grain sizes, thus paving the way to simultaneously improve the hardness and toughness of composite carbide ceramics. A wide range of composite carbides can be prepared, but their complex microstructure evolution during aging makes performance optimization extremely challenging. In this work, a strategy by combining the multiscale simulations and experiments is proposed to systematically study the influence of the composition and process on the spinodal decomposition structure and performance. Taking (Ti, Zr)C carbide ceramics as a representative example, three distinct compositions of (Ti, Zr)C solid solutions were successfully synthesized via a sol-gel combined with spark plasma sintering method at 1800 °C, guided by thermodynamic calculations. The influence of aging temperature and duration on spinodal decomposition microstructure evolution in (Ti, Zr)C carbide ceramics was studied by integrating phase-field simulations and first-principles calculations with key experimental observations. After spinodal decomposition, numerous nanoscale nodular structures form, accompanied by the generation of dislocations, leading to a significant improvement in both hardness and toughness of the composite carbides. After aging at 1300 °C for 3 h, the composite carbides achieved peak hardness at 2436 HV, accompanied by a fracture toughness of 3.24 MPa·m<sup>1/2</sup>. This research provides a scientific approach to improving the hardness and toughness of carbide ceramics through spinodal decomposition, offering essential theoretical foundations for microstructural control and synergistic optimization of performance in innovative carbide ceramics.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"282 ","pages":"Article 120487"},"PeriodicalIF":8.3,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142451532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-20DOI: 10.1016/j.actamat.2024.120496
Fei Shen Ong , Kohta Nambu , Kenta Kawamura , Kohei Hosoi , Hiroshi Masuda , Bin Feng , Koji Matsui , Yuichi Ikuhara , Hidehiro Yoshida
This study demonstrates the successful fabrication of near-full density monophasic tetragonal 1.5-mol% yttria-stabilized zirconia (1.5YSZ) ceramics using current-ramp flash (CRF) sintering technique. The process involved regulating Joule heating in the samples by fine-tuning the input power through an alternating current field (nominal current density: 50 mA·mm−2) within a 3-min timeframe at a furnace temperature of 1100°C. This approach effectively enhanced grain size uniformity, which is crucial for preventing sample cracking associated with spontaneous tetragonal-to-monoclinic (T→M) phase transformation, thereby promoting densification with average relative densities exceeding 99%. The highest average fracture toughness of the 1.5YSZ samples was measured at 9.2 MPa·m0.5 using the standardized single-edge pre-cracked beam method. This toughness is approximately double that of commonly used 3YSZ samples produced by CRF sintering, all of which exhibited comparable average grain sizes and relative densities. Additionally, the 1.5YSZ samples demonstrated nearly identical resistance to low-temperature degradation (LTD) compared to the 3YSZ samples after accelerated hydrothermal aging at 140°C for 15 h, roughly equivalent to 60 years at 37°C. The reduced yttria concentration in 1.5YSZ facilitates T→M phase transformation at lower stress thresholds, enhancing toughness through increased crack shielding from a larger volume fraction of transformed grains. Furthermore, the uniform yttria distribution in 1.5YSZ, revealed by scanning transmission electron microscopy, compensates for the reduced tetragonal phase stability and contributes to improved LTD resistance. Notably, these exceptional properties were achieved at a furnace temperature 300°C lower and with a sintering duration several hours shorter than those of conventionally-sintered counterparts.
{"title":"Realizing near-full density monophasic tetragonal 1.5-mol% yttria-stabilized zirconia ceramics via current-ramp flash sintering","authors":"Fei Shen Ong , Kohta Nambu , Kenta Kawamura , Kohei Hosoi , Hiroshi Masuda , Bin Feng , Koji Matsui , Yuichi Ikuhara , Hidehiro Yoshida","doi":"10.1016/j.actamat.2024.120496","DOIUrl":"10.1016/j.actamat.2024.120496","url":null,"abstract":"<div><div>This study demonstrates the successful fabrication of near-full density monophasic tetragonal 1.5-mol% yttria-stabilized zirconia (1.5YSZ) ceramics using current-ramp flash (CRF) sintering technique. The process involved regulating Joule heating in the samples by fine-tuning the input power through an alternating current field (nominal current density: 50 mA·mm<sup>−2</sup>) within a 3-min timeframe at a furnace temperature of 1100°C. This approach effectively enhanced grain size uniformity, which is crucial for preventing sample cracking associated with spontaneous tetragonal-to-monoclinic (T→M) phase transformation, thereby promoting densification with average relative densities exceeding 99%. The highest average fracture toughness of the 1.5YSZ samples was measured at 9.2 MPa·m<sup>0.5</sup> using the standardized single-edge pre-cracked beam method. This toughness is approximately double that of commonly used 3YSZ samples produced by CRF sintering, all of which exhibited comparable average grain sizes and relative densities. Additionally, the 1.5YSZ samples demonstrated nearly identical resistance to low-temperature degradation (LTD) compared to the 3YSZ samples after accelerated hydrothermal aging at 140°C for 15 h, roughly equivalent to 60 years at 37°C. The reduced yttria concentration in 1.5YSZ facilitates T→M phase transformation at lower stress thresholds, enhancing toughness through increased crack shielding from a larger volume fraction of transformed grains. Furthermore, the uniform yttria distribution in 1.5YSZ, revealed by scanning transmission electron microscopy, compensates for the reduced tetragonal phase stability and contributes to improved LTD resistance. Notably, these exceptional properties were achieved at a furnace temperature 300°C lower and with a sintering duration several hours shorter than those of conventionally-sintered counterparts.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"283 ","pages":"Article 120496"},"PeriodicalIF":8.3,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142451524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-20DOI: 10.1016/j.actamat.2024.120494
C. Hu , Y.X. Liu , B.B. He , M.X. Huang
Austenitic steels are renowned for exceptional ductility and toughness, yet their widespread application is hindered by low strength. Enhancing their strength while preserving ductility is crucial for scientific and industrial purposes. In this study, we successfully fabricated heterostructured austenitic steels via stepwise controllable precipitation and recrystallization and break the strength-ductility trade-off. Initial precipitation induces nonshearable B2 nanoprecipitates within the austenitic matrix, and subsequent partial recrystallization introduces intermetallic B2 networks along deformation bands. Advanced characterizations verify that the dense nanoprecipitates in the matrix confer high strength, while the networks accommodate strain through nanoparticle formation and anisotropic plastic deformation of the B2 phase, as well as the stacking faults and mechanical twins within austenite. Collectively, these mechanisms contribute to a high yield strength of 1200 MPa and good ductility of 25%, exceeding previous high-performance austenitic steels. This work can provide insights into the design of strong and ductile austenitic steels and the processing-microstructure-property relationship of heterostructured materials.
{"title":"Role of intermetallic networks in developing high-performance austenitic steel","authors":"C. Hu , Y.X. Liu , B.B. He , M.X. Huang","doi":"10.1016/j.actamat.2024.120494","DOIUrl":"10.1016/j.actamat.2024.120494","url":null,"abstract":"<div><div>Austenitic steels are renowned for exceptional ductility and toughness, yet their widespread application is hindered by low strength. Enhancing their strength while preserving ductility is crucial for scientific and industrial purposes. In this study, we successfully fabricated heterostructured austenitic steels via stepwise controllable precipitation and recrystallization and break the strength-ductility trade-off. Initial precipitation induces nonshearable B<sub>2</sub> nanoprecipitates within the austenitic matrix, and subsequent partial recrystallization introduces intermetallic B<sub>2</sub> networks along deformation bands. Advanced characterizations verify that the dense nanoprecipitates in the matrix confer high strength, while the networks accommodate strain through nanoparticle formation and anisotropic plastic deformation of the B<sub>2</sub> phase, as well as the stacking faults and mechanical twins within austenite. Collectively, these mechanisms contribute to a high yield strength of 1200 MPa and good ductility of 25%, exceeding previous high-performance austenitic steels. This work can provide insights into the design of strong and ductile austenitic steels and the processing-microstructure-property relationship of heterostructured materials.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"283 ","pages":"Article 120494"},"PeriodicalIF":8.3,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142451515","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
扫码关注我们
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号